The present invention relates to a method for forming a film pattern on a substrate.
As a method for producing a desired pattern on a substrate using light without a photoresist, laser processing is well known by means of a YAG laser (the wavelength is 1.06 microns). In this process, a substrate with a film to be patterned is irradiated with a spot laser beam which is moved along a line on the substrate to produce a groove as congregation of spots by removing a portion of the film by the energy of the laser beam. Because of this, the scanning speed and the energy density of the laser beam must be chosen finely in correspondence to the thermal conductivity and the sublimability of the film to be processed. So it is difficult to manufacture products within the specification determined for this product without lowering the yield. Further, the laser beam from a YAG laser conveys only the photon energy of 1.23 eV and the pulse width is no shorter than 80 namo seconds in order to give a sufficient energy to the film. The beam energy tend to disperse on the film, e.g., a metallic film or transparent conductive film both having a large thermal conductivity while an underlying insulating substrate, e.g., a glass substrate, has a conductivity smaller than that of the film by more than one order of magnitude. Namely, the energy applied to the part to be removed in dissipated to heat the neighboring part of the film.
In the laser machining with a YAG laser by means of Q-switching, a film on a substrate must be scanned at a scanning speed of 30-60 cm/min with strong laser beam with an average power of 0.5-1 W in the case that the spot diameter is 50 micron meters, the pulse frequency is 3 KHz, and the pulse width is 100 namo seconds. As a result, the underlying surface is likely damaged by the high energy and causes micro-cracks thereon in the form of scales similar to the configuration of section view of laser beam.
Further, because of laser beam with a long wavelength, the machined portion tend to bulge its edge. Particularly, in the case of process of a metallic thin film, liquid metal appears on the edge due to the transmission of thermal energy in a lateral direction, and forms a swell portion due to the surface tension of the liquid metal. For this reason, a sharp edge can not obtained. In addition, when Q-switcing is used, the maximum value of the laser energy is apt to fluctuate during long use so that the condition must be checked before every use.
Still further, it is entirely impossible to produce selectively fine patterns with a very narrow interval of 10 to 50 microns on a same substrate. And frequently the patterning may be only in insufficient manner so that additional etching must be carried out with an etchant solution.
A related patent application has been filed with Japanese Patent Office. The application number is sho 59-211769.